Modulated supply stage with feedback to switched supply

ABSTRACT

There is disclosed a voltage supply stage comprising: a selection means for selecting one of a plurality of power supply voltages in dependence on a reference signal representing a desired power supply voltage; a combining means for combining the selected power supply voltage with a correction signal to generate an adjusted power supply voltage; and an adjusting means adapted to generate the correction signal in dependence on the reference signal and the adjusted power supply voltage, wherein the selection means is arranged to select the one of the plurality of supply voltages further in dependence on a signal derived from one of the inputs to the combining means.

CROSS-REFERENCE TO RELATED APPLICATIONS

The instant application is a Continuation of U.S. patent applicationSer. No. 12/991,695, with a 371(c) date of Jun. 13, 2011, and isincorporated herein by reference.

BACKGROUND TO THE INVENTION

1. Field of the Invention

The present invention relates to a modulated supply stage, andparticularly to such a stage in which a feedback loop is connected toprovide an input to control selection of a low frequency switchedsupply. The feedback may be provided from the output of the lowfrequency switched supply stage or from the output of a high frequencycorrection stage.

2. Description of the Related Prior Art

It is known by those skilled in the art that envelope tracking (ET) andenvelope elimination and restoration (EER) can give large improvementsin efficiencies of power amplifier operation, particularly with signalssuch as orthogonal frequency-division multiplexing (OFDM) which havelarge crest factors. However, it is also known that the application ofthese techniques presents considerable difficulties due to the largepowers and bandwidths involved. These difficulties become particularlyformidable when applied to portable wireless terminals where the numberof discrete components must be minimised and large dimensioned magneticsmust be avoided.

An apparently simple solution would be to make the modulator a fastresponding linear regulator. However, this would simply change powerwasted in the power amplifier with that wasted in the linear regulator,resulting in no net gain in efficiency.

In order to gain some efficiency, some prior art implementations havebeen known to follow the switched mode supply with a low drop-out (LDO)fast responding linear regulator. This removes the errors inherent inthe switched mode operation. However a problem arises in that there mustbe sufficient range in the linear regulator to allow for the peaks inthe switched mode error, which can be considerably larger than the rootmean square (RMS) error. This results in a large standing dissipation inthe LDO.

A significant improvement on this is provided by techniques disclosed inGB2398648. This implementation is shown in FIG. 1. FIG. 1 shows adiagram of a typical switched mode power supply used as an efficientpower conversion means. It must be noted that this is given as anexample; the invention is not restricted to topologies of this type.

A coarse DC-DC switched supply 102 provides an approximation to therequired waveform, provided as a reference waveform on input line 118,after filtering with filter network 104. The filter comprises aninductor 106 for storage of magnetic energy, and a capacitor 108 forstorage of electric energy. A transformer 110 is used which can givetrue summation, e.g. signals can be added and subtracted, so the meancorrection from a correction amplifier 114 can be set to zero,eliminating large standing dissipation. The output of the transformerprovides an output to a load 112. The output of the transformer 110 isfedback to provide an input to the correction amplifier 114, whichreceives as a further input a reference signal on line 116 (which may bethe same as, or derived from the same source as, the reference signal online 118). The transformer combines the switched supply voltage with theoutput of the correction amplifier to provide a corrected outputvoltage.

A potential problem with the architecture of FIG. 1 is that thetransformer 110 has to have a high self-inductance to prevent shuntingof the correction current through the unwanted inductance of thetransformer. This means that large ferrite cores must typically be used.Whilst this is acceptable for wireless infrastructure implementations,this presents particular difficulties for portable handsetimplementations or any implementation where size restrictions may apply.

The supply stage of FIG. 1 is capable of very efficient operation, butthe circuit can only be switched between two levels: intermediate levelscan only be obtained by the filtering action of the energy storageelements 106 and 108. For low frequency outputs (frequencies much lessthan the switching frequencies), this arrangement will be able toperform tracking, but the circuit may provide poor tracking at highfrequency. There will also be substantial breakthrough of switchingrelated products at high frequencies. When the said power conversioncircuit is used as a modulator, the energy storage elements form aparallel resonant tank which will present a high impedance to the loadat some frequencies.

The effect of this can be seen in FIG. 2. The reaction of the energystorage elements to the rapidly changing current demand produces awaveform 204 at the power amplifier. This shows severe mistracking whencompared with the wanted waveform 202. Also, the high output impedancemay result in instability of the load.

Examples of prior art switched mode modulators can be found in U.S. Pat.Nos. 5,905,407, 6,054,914, 6,198,374, 6,300,826, 6,583,664, 6,661,210,6,661,217, 6,710,646, 6,792,252, and in US Patent application No.2002/0008574.

It is an aim of the invention to provide an improved modulated powersupply stage.

SUMMARY OF THE INVENTION

In one aspect the invention provides a voltage supply stage comprising:a selection means for selecting one of a plurality of power supplyvoltages in dependence on a reference signal representing a desiredpower supply voltage; a combining means for combining the selected powersupply voltage with a correction signal to generate an adjusted powersupply voltage; and an adjusting means adapted to generate thecorrection signal in dependence on the reference signal and the adjustedpower supply voltage, wherein the selection means is arranged to selectthe one of the plurality of supply voltages further in dependence on asignal derived from one of the inputs to the combining means.

The inputs to the combining means are the signals to be combined: theselected power supply voltage and the correction signal. The selectedpower supply voltage is the output of the selection means, which ispreferably a switched voltage supply. The correction signal is theoutput of the adjustment means.

The signal derived from one of the inputs to the combining means may bethe output of the selection means.

The signal derived from one of the inputs to the combining means may bethe output of the adjusting means.

A feedback control stage may provide the signal derived from one of theinputs to the combining means to the selection means. The feedbackcontrol stage may be adapted to receive as a first input the referencesignal and as a second input one of the inputs to the combining means,and further adapted to adjust the reference signal in dependence on theone of the inputs to the combining means to provide an adjustedreference signal for the selection means.

In an embodiment the feedback control stage may comprise: a subtractorfor subtracting the output of the selection means from the referencesignal; a proportional-integral, PI, controller for receiving thesubtracted signal and generating a modified output, and a summer foradding the modified output of the PI controller to the reference signal,to form the output of the feedback control stage being the adjustedreference signal.

In an alternate embodiment the feedback control stage may comprise: aproportional-integral, PI, controller for receiving the output of theadjusting means and generating a modified output, and a summer foradding the modified output of the PI controller to the reference signal,to form the output of the feedback control stage being the adjustedreference signal.

The combining means preferably comprises an inductor, and the adjustmentmeans preferably comprises a voltage-to-current converter, wherein acurrent representing the correction signal is injected at the secondterminal of the inductor to adjust the current flowing in the inductorprovided by the selected power supply voltage, a thus adjusted currentflowing in a load connected to the second terminal of the inductor tothereby develop the adjusted supply voltage across said load.

The voltage supply stage preferably comprises a reference adjustmentstage for adjusting the reference signal to provide a modified referencesignal. The selection means may be adapted to select in dependence onthe modified reference signal. The feedback control means may be adaptedto provide the signal derive from one of the inputs to the combiningmeans in dependence on the modified reference signal.

The reference adjustment stage may comprise a means for adjusting theamplitude of the reference signal in dependence upon a differencebetween the amplitude of the reference signal and the amplitude of theselected supply voltage. The means for adjusting the amplitude of thereference signal may include: a correlator for determining the amplitudeerror between the reference signal and the selected supply voltage; andan amplitude adjustment block for modifying the reference signal independence on said error. The reference adjustment stage may comprise ameans for controlling a current flow in the combining means to maximizecurrent slow in the combining means and thereby minimize current flow inthe adjustment means. The means for controlling the current flow mayinclude: a correlator for determining the current flow in the inductorand for providing a control signal to modify coefficients of adifferentiator in dependence thereon, the differentiator being arrangedto receive the reference signal and generate a differentiated versionthereof. The differentiator may be arranged to receive as an input theamplitude adjusted reference signal generate a differentiated amplitudeadjusted reference signal, the reference adjustment stage furthercomprising a summer for summing the amplitude adjusted reference signalwith the differentiated amplitude adjusted reference signal to form themodified reference signal.

A tracking modulated power supply stage for a mobile wireless devicepreferably includes a voltage supply stage as defined.

In this aspect the invention also provide a method for generating asupply voltage comprising: selecting one of a plurality of power supplyvoltages in dependence on a reference signal representing a desiredpower supply voltage; combining the selected power supply voltage with acorrection signal to generate an adjusted power supply voltage;generating the correction signal in dependence on the reference signaland the adjusted power supply voltage; and providing as a feedbacksignal one of the input signals to the combining step, wherein theselecting step is further arranged to select the one of the plurality ofsupply voltages in dependence on the feedback signal.

The providing step may provide the output of the selection means as thefeedback signal. The providing step may provide the output of theadjusting means as the feedback signal.

The method may further comprise the step of controlling the feedbacksignal for providing the signal derived from one of the inputs to thecombining means to the selection means.

The step of controlling the feedback may comprise receiving as a firstinput the reference signal and as a second input one of the inputs tothe combining step, and adjusting the reference signal in dependence onthe one of the inputs to the combining step to provide an adjustedreference signal for the selecting step.

The step of controlling the feedback may comprise: subtracting theoutput of the selection means from the reference signal; receiving thesubtracted signal and generating a proportional-integral, PI, modifiedoutput, and adding the modified output to the reference signal, to formthe adjusted reference signal.

The step of controlling the feedback may comprise: receiving the outputof the adjusting means and generating a proportional-integral, PI,modified output, and adding the modified output to the reference signal,to form the adjusted reference signal.

The combining means may comprise an inductor, and the adjustment meansmay comprise a voltage-to-current converter, the method further maycomprise injecting a current representing the correction signal at thesecond terminal of the inductor to adjust the current flowing in theinductor provided by the selected power supply voltage, a thus adjustedcurrent flowing in a load connected to the second terminal of theinductor to thereby develop the adjusted supply voltage across saidload.

The method may further comprise the step of adjusting the referencesignal to provide a modified reference signal.

The selecting step may be adapted to select in dependence on themodified reference signal.

The feedback control step may be adapted to provide the signal derivedfrom one of the inputs to the combining step in dependence on themodified reference signal.

The step of adjusting may include adjusting the amplitude of thereference signal in dependence upon a difference between the amplitudeof the reference signal and the amplitude of the selected supplyvoltage.

The step of adjusting the amplitude of the reference signal may include:determining the amplitude error between the reference signal and theselected supply voltage; and modifying the reference signal independence on said error.

The step of adjusting may comprise controlling a current flow in thecombining means to maximize current flow in the combining means andthereby minimize current flow in the adjustment means.

The step of controlling the current flow may include: determining thecurrent flow in the inductor and for providing a control signal tomodify coefficients of a differentiator in dependence thereon, thedifferentiator being arranged to receive the reference signal andgenerate a differentiated version thereof.

The method may further comprise the steps of: receiving at thedifferentiator as an input the amplitude adjusted reference signal; andgenerating a differentiated amplitude adjusted reference signal, theadjustment step further comprising summing the amplitude adjustedreference signal with the differentiated amplitude adjusted referencesignal to form the modified reference signal.

In another aspect the invention provides a combiner for combining afirst voltage signal with a second voltage signal to provide a combinedvoltage signal, comprising: an inductor having a first terminalconnected to the first voltage signal; a load connected to the secondvoltage terminal; and a conversion means for receiving at an input thesecond voltage signal and generating at an output a current representingthe second voltage signal, the output of the conversion means beingconnected to the second terminal of the inductor, wherein a current isgenerated in the load representing the combined first and secondvoltages, the combined voltage signal thus being developed across theload.

The combiner may further comprise a capacitor connected at the secondterminal of the inductor, wherein in combination the inductor and thecapacitor form an L-C filter for the combined signal.

The conversion means may be a voltage-to-current converter.

The load may be a power amplifier, and the combined voltage is a supplyvoltage for the power amplifier.

A modulated voltage supply may comprise a combiner as defined, and mayfurther comprise: a selection means for selecting one of a plurality ofpower supply voltages in dependence on a reference signal, the selectedsupply being the first voltage signal, the conversion means being anadjusting means for generating a correction signal comprising the secondvoltage signal in dependence on the reference signal and the combinedvoltage signal.

In this aspect the invention also provides a method for combining afirst voltage signal with a second voltage signal to provide a combinedvoltage signal, comprising: connected to the first voltage signal to afirst terminal of an inductor; connecting a load to the second terminalof the inductor; converting the second voltage signal into a currentrepresenting the second voltage signal; providing the currentrepresenting the second voltage signal at the second terminal of theinductor, wherein a current is generated in the load representing thecombined first and second voltages, the combined voltage signal thusbeing developed across the load.

The step of providing the current representing the second voltage signalat the second terminal of the inductor may comprise injecting currentinto the second terminal of the inductor.

In a further aspect the invention provides a voltage supply stagecomprising: a selection means for selecting one of a plurality of powersupply voltages in dependence on a reference signal representing adesired power supply voltage; a combining means for combining theselected power supply voltage with a correction signal to generate anadjusted power supply voltage; a correction means adapted to generatethe correction signal in dependence on the reference signal and theadjusted power supply voltage; an adjustment means for adjusting theamplitude of the reference signal in dependence on a difference betweenthe amplitude of the reference signal and the amplitude of the selectedsupply voltage; and differentiation means for controlling the current inthe combining means to maximize the current flowing in the combiningmeans and thereby minimize the current required to flow in thecorrection means.

The adjustment means may include: a correlator for determining anamplitude error between the reference signal and the selected supplyvoltage; and an amplitude adjustment block for modifying the referencesignal in dependence on said error.

The means for controlling the current in the combining means to maximizethe current flowing in the combining means and thereby minimize thecurrent flowing in the correction means may include a correlator fordetermining the current flow in the inductor and for modifyingcoefficients of a differentiator in dependence thereon.

The amplitude adjustment block may receive the reference signal andgenerates the amplitude adjusted reference signal, the differentiatorreceives the amplitude adjusted reference signal and generates adifferentiated version thereof at its output, and a summer sums theamplitude adjusted reference signal and the modified differentiatedreference signal to provide the reference signal for use by themodulated power supply stage.

In this further aspect the invention also provides a method for agenerating a modulated supply voltage, comprising: selecting one of aplurality of power supply voltages in dependence on a reference signalrepresenting a desired power supply voltage; combining the selectedpower supply voltage with a correction signal to generate an adjustedpower supply voltage; generating the correction signal in dependence onthe reference signal and the adjusted power supply voltage; adjustingthe amplitude of the reference signal in dependence on a differencebetween the amplitude of the reference signal and the amplitude of theselected supply voltage; and controlling the current in the combiningmeans by differentiation to maximize the current flowing in thecombining means and thereby minimize the current required to flow in thecorrection means.

The adjustment step may include: determining an amplitude error betweenthe reference signal and the selected supply voltage; and modifying thereference signal in dependence on said error.

The controlling the current in the combining means to maximize thecurrent flowing in the combining means and thereby minimize the currentflowing in the correction means may include determining the current flowin the inductor and modifying coefficients of a differentiator independence thereon.

The amplitude adjustment block may receive the reference signal andgenerate the amplitude adjusted reference signal, the differentiator mayreceives the amplitude adjusted reference signal and generates adifferentiated version thereof at its output, and a summer sums theamplitude adjusted reference signal and the modified differentiatedreference signal to provide the reference signal for use by themodulated power supply stage.

All aspects and feature of the invention as defined or as discussed inthe following description may be implemented individually or in anycombination.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described by way of example with reference tothe accompanying figures in which:

FIG. 1 illustrates a modulated power supply stage including a lowfrequency switched supply and a high frequency error correction inaccordance with the prior art;

FIG. 2 illustrates a problem associated with a prior art arrangementsuch as FIG. 1;

FIG. 3 illustrates an improvement in a modulated power supply stage inaccordance with a first exemplary embedment of the invention;

FIG. 4 illustrates a modification to the preferred implementation of thefirst embodiment;

FIG. 5 illustrates a further modification to the preferredimplementation of the first embodiment;

FIG. 6 illustrates an exemplary implementation of a second embodiment ofthe invention; and

FIG. 7 illustrates an exemplary implementation of embodiments of theinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will now be described by way of example with reference toits application in various embodiments. One skilled in the art willappreciate that the invention is not limited in its scope to thespecifics of implementation details of any particular embodiment.

The broad principle in accordance with the invention is to provide anadditional feedback path. The feedback path provides an input to theswitched supply.

The provision of the feedback path is in accordance with one of twobroad embodiments. In a first broad embodiment the feedback pathoriginates from the output of the switched supply, i.e. the output of acoarse path. In a second broad embodiment the feedback path originatesfrom the output of the correction path. Thus the switched supply stageis provided an input derived from an input to the combiner stage forcombining the switched supply with the correction signal. This feedbackreduces errors at low frequencies, and allows the bandwidth of thecombiner stage to be reduced.

A first arrangement for the implementation of the first broad embodimentis now described with reference to FIG. 3. Like reference numerals areused in the following figures where any element corresponds to anelement shown in another figure.

The modulated supply stage of FIG. 3, generally denoted by referencenumeral 300, comprises a switched supply stage 302, a switched supplycontroller 304, a correction amplifier 310, a combiner stage 308, afeedback control stage 306, a capacitor 312 and a load 314.

Modulated supply stage 300 of FIG. 3 provides a modulated supply on anoutput line 318 to the load 314 in dependence on a reference signalprovided on input line 316. The load 314 may be a power amplifier.

The switched supply controller 304 receives an input signal from thefeedback control stage 306. In dependence upon the signal from thefeedback control stage 306, the switched supply controller 304 controlsthe switched supply 302 to provide a switched supply output on line 320.The switched supply output on line 320 provides a first input to thecombiner stage 308.

The feedback control stage 306 receives two inputs: a first input isprovided on line 322 from the output of the switched supply stage 302 online 320, and a second input is provided by the reference signal on theinput line 316. The feedback control stage 306 operates to adjust thereceived reference signal in dependence upon the feedback signal toprovide a modified input to the switched supply controller 304.

A second input to the combiner stage 308 is provided by the output ofthe correction amplifier 310. The correction amplifier 310 receives as afirst input the reference signal on line 316, and receives as a secondinput a feedback signal on line 324 comprising the output of thecombiner stage 308 on line 318.

An optional capacitor 312 is connected between the output line 318 andground.

In the example arrangement of FIG. 3, in accordance with the firstembodiment, the combiner stage 308 is implemented as a transformer. Thetransformer has a first winding 340 and a second winding 342. A firsttap of the first winding 340 is connected to the output of the switchedsupply stage 302 on line 320. A second tap of the first winding 340provides the output signal on line 318. A first tap of the secondwinding 342 is connected to receive the output of the correctionamplifier 310. A second tap of the second winding 342 is connected toground. In this way, the transformer combines the output of the switchedsupply with the output of the correction amplifier to generate acorrected switched supply at its output.

The feedback control stage 306 operates to utilise the feedback on line322 from the output of the switched supply to provide an improvedversion of the reference signal on line 316 to the input of the switchedsupply controller 304. The feedback control stage 306 includes asubtractor 326, a summer 330, and a PI control block 328. The subtractorreceives the reference signal on line 316 as one input and the feedbacksignal on 322 as another input. The feedback signal on line 322 issubtracted from the reference signal on line 316 to provide an input tothe PI control block 328. The implementation of a PI(proportional-interval) controller is well-known in the art. The outputof the PI control block 328 forms a first input to the summer 330, thesecond input to the summer 330 being provided by the reference signal online 316. The summer adds the output of the PI control block 328 to thereference signal 316, to generate a modified reference signal for theswitched supply controller 304 as the output of the feedback controlstage 306. The summer 330 adds a feedforward element to the feedbackcontrol, which is needed as large amplitude signals are being handled.

The feedback control stage 306 operates by sensing differences in levelusing subtracting means 326. The output level from the subtractor 326 issensed by the PI control block 328 and used to provide a slow adjustmenttrim to the input level to the switched supply controller 304 so thatboth levels are as close as possible.

The feedback provided in the switched supply stage path on line 322removes low frequency errors in the switched supply output on line 320such that the combiner stage 308 may be implemented as a smaller devicethan would otherwise be possible.

The switched supply controller 304 controls the switched supply toselect the appropriate supply voltage in accordance with techniquesknown in the art. The switched supply controller controls the switchedsupply 302 in accordance with the signal on its input line, which in theillustrated arrangement is provided by the output of the feedbackcontrol stage 306.

In a modified arrangement, the combiner stage 308 is implemented as aninductor rather than as a transformer. This modified implementation isshown in FIG. 4.

As illustrated in FIG. 4, the combiner stage 308 is provided with aninductor 402 having a first terminal connected to the output line 320 ofa switched supply stage 302. A second terminal of the inductor 402provides the output signal on line 318.

Implementing the combiner stage 308 as an inductor, an additionalmodification is provided to achieve the combining function. Thecorrection amplifier 310 of FIG. 3 is replaced by the correctionamplifier 410 of FIG. 4. The correction amplifier 410 provides a currentoutput on line 412, which injects current at the terminal of theinductor 402 which is connected to the output line 318. This providesthe function of combining the correction signal with the switched supplysignal to obtain a modified modulated supply voltage on line 318.

The inductor 402 of the exemplary arrangement of FIG. 4 has twofunctions. Firstly, the inductor combines the switched supply signalwith the correction (or adjustment) signal. Secondly, the inductor 402may combine with the capacitor 312 to provide the L-C filter provided byinductor 106 and capacitor 108 in FIG. 1.

In comparison to the architecture of GB2398648, the magnetising or selfinductance of the inductor 402 is used as part of the circuit function,rather than being an unwanted but necessary additional means, as in thetransformer arrangement of FIG. 3. Where the L-C arrangement as shown inFIG. 1 is provided, the inductor 106 may implement the inductor 402, andthe capacitor 108 may implement the capacitor 312. Thus the combiner isimplemented using existing circuitry. This suggests that the bandwidthrequirement of the output combining circuit is much reduced.

Another significant different between the architecture of FIG. 3 andthat of FIG. 4 is that most of the output current is shunted through theinductor 402 by the switched supply stage rather than being provided bythe correction amplifier.

In general, with reference to FIG. 4, the switched supply 302 switchesbetween a set of voltages under the control of the switched supplycontrol block 304, to select the switched supply corresponding to thereference signal voltage on line 316. The correction amplifier 410provides an adjustment or correction signal as a current, which is addedto the current flowing in the output at the inductor 402 on line 318representing the switched supply voltage. The adjusted current on line318 develops an adjusted supply voltage for the load 314.

The additional elements of FIG. 4 are provided as preferred elements toenhance the operation of the arrangement of FIG. 3. The implementationof the combiner stage 308 as an inductor, with a current injectingcorrection amplifier, is not dependent on the feedback provided on line322. This arrangement may advantageously be implemented independent ofthe provision of feedback for the switched supply stage.

With reference to FIG. 5, there is illustrated a still furthermodification in an exemplary arrangement.

With reference to FIG. 5, the modulated supply stage 500 illustratedtherein is additionally provided with a reference adjustment stage 403.

The reference adjustment stage is adapted to receive as an input thereference signal on line 316. The reference adjustment stage 403additionally receives a further input being a feedback signal on line416 derived from the output of the correction amplifier 410 on line 412.The reference adjustment stage 403 generates an output which forms aninput to the feedback control stage 306. In the arrangement of FIG. 5,rather than the feedback control stage 306 receiving the referencesignal on line 316 as a direct input, the feedback control stage 306receives a modified version of such reference signal provided as theoutput of the reference adjustment stage 402.

The reference adjustment stage 403 includes an amplitude adjustmentblock 404, a differentiator block 406, a summer 408, a correlator 411,and two integrators 413 and 414.

The correlator 411 receives as a first input the reference signal online 316, and as a second input the output of the correction amplifier410 on line 416. The correlator generates two outputs. The first outputis provided to the amplitude adjustment block 403 via an integrator 413.A second output is provided to the differentiator block 406 via anintegrator 414. The amplitude adjustment block receives as an input thereference signal on line 316, in addition to the integrated first outputof the correlator 411. The differentiator block 406 receives the outputof the amplitude adjustment block 403 as a first input, and the secondintegrated output of the correlator 411 as a second input. The summer408 receives as a first input the output of the amplitude adjustmentblock 401, and as a second input the output of the differentiator block406. The output of the summer 408 forms the output of the referenceadjustment stage 403, providing the input to the feedback control stage306.

The correlator 411 correlates the reference signal current on line 316with the current provided by the correction amplifier 410 on line 416.The correlator 411 provides a positive output when both input signalscorrelate, and a negative output when both input signals are inanti-correlation. Two outputs are generated from the correlator 411depending on the selection of differently shaped filter responsespresent at the correlator input. Thus the correlator is controlled, bymeans not shown, to apply its input signals to one of two sets offilters.

The differentiator 406 is controlled by the correlator when the filterresponse of the correlator input is selected to have a bandpassresponse. The amplitude adjustment block 404 is controlled by thecorrelator when the filter response of the correlator input is selectedto have a low pass response. The correlator thus generates two outputs,which outputs form inputs to the integrators 413 and 414.

The integrator 414 integrates up the correlator output allowing it tosteer the differentiator coefficients of the differentiator 406 in acontrolled manner.

The reference adjustment stage 403 provides a two-fold functionality. Afirst functionality is provided by the differentiator 406, and a secondfunctionality is provided by the amplitude adjustment block 404.

In general, the differentiator 406 operates to maximise the currentflowing through the inductor 402. This minimises the current required tobe delivered by the correction amplifier 410, as discussed in furtherdetail below.

In general, the amplitude adjustment block 404 operates to minimise therequirements of the correction amplifier 410 to provide the amplitudecorrections, so that the correction amplifier can work less-hard, asdiscussed in further detail below.

The voltage at the first terminal of the inductor 402 is the output ofswitched supply 302 which may be approximated as ax₁+b.dx/dt where a₁ isthe wanted signal output of the modulator, dx/dt represents thetime-derivative correction signal, and b is the amplitude of thetime-derivative correction signal.

The voltage at the second terminal of the inductor is the voltage at thefirst terminal corrected by the action of the correction amplifier suchthat it is maintained as closely as possible to a voltage signal whichmay be represented by ax₂ where ax₂ is the wanted modulator output.

The differentiator 406 operates to control the amplitude component b ofthe voltage signal delivered to the load. The correlator 411 providesthe differentiator 406 with information as to the current flowing in theinductor 402. Based on that current information, the coefficients of thedifferentiator are adjusted to ensure the voltage level b is the correctlevel. The differentiation in block 406 is then changed. Thedifferentiator thus improves the signal to be nearer the voltage that iswanted.

Without the differentiator 406, there is a dc current flow (but no accurrent flow) through the inductor 402 due to the switched supplyfeedback path.

The differentiator 406 is provided to ensure most of the current flows,not just the dc current flow, through the inductor 402.

The current correlator 411 multiplies the AC current provided by thecorrection amplifier 410 with the AC component of the reference signalon line 316. If the time derivative of the reference signal is too low,the correction amplifier current correlates. If the derivative term istoo high, there is anti-correlation between the two signals. This can beused to adjust the link between the measured load current and thederivative terms. The second order terms will not need adjusting.

The implementation of a differentiator such as differentiator 406, andthe adaptation of differentiator coefficients, is known to one skilledin the art.

The operation of the differentiator 406, to obtain performanceimprovements, can be further understood as follows.

The switched supply 302 is used as the primary tracking element, withthe correction amplifier 410 applying a fine adjustment or correction.The switched supply 302 runs closed loop for improved tracking based onthe feedback path 322. There will still be some residual errors presentin the output of the switched supply. The correction amplifier providesanother closed loop that removes the residual errors present in theoutput of the switching supply. The correction amplifier can remove highfrequency errors, but low frequency correction is impaired by theshunting effect of the self inductance of the inductor 402. However, theswitched supply loop has higher loop gain at low frequencies, socorrection can be curtailed at lower frequencies.

The reference adjustment stage 403 addresses a problem which arises whenboth feedback loops force both sides of the inductor 402 to be equal.This would force the voltage across the inductor 402 to be zero. As aresult of this, the correction amplifier 410 would be required to sourcethe entire AC part of the current in the inductor 402. In order to forceAC current to flow through the inductor 402, the voltage across theinductor 402 must be equal to the inductance multiplied by the timederivative of the current flowing through the inductor 402. The currentthrough the inductor 402 is the current through the load 314, and bydefinition the voltage output of an envelope tracking modulator mustfollow this current. Therefore, if the input to the switched supply 302follows the time derivative term as well as the modulation signal, thenit is possible for the switched supply 302 to supply most of the ACcurrent besides the DC, thus reducing the power needed to be deliveredby the correction amplifier 410.

The capacitor 312 connected at the output results in a component ofvoltage across the inductor 402 being equal on the second derivative ofthe applied modulation voltage. This means that ideally the signalapplied to the switched supply 302 should have first and secondderivative terms. The second derivative terms are fixed by the inductorand capacitor values used, but the first derivative is also a functionof the current drawn by the load 314. Therefore some measure of loadcurrent is required, and the derivative terms are linked to this loadcurrent.

The link between the load current and this derivative term isestablished by means of the correlator 411, as discussed above.

The amplitude adjustment block 404 operates to ensure that the amplitudeof the dc signal across the inductor 402 is zero, i.e. the amplitude atthe two terminals of the inductor is zero. The amplitude adjustmentblock 404 thus operates to attempt to make a₁ equal to a₂. If a1 and a2are made equal, then the voltage signal developed at the second terminalof the inductor, for delivery to the load, is provided by the componentb.dx/dt only.

If such an objective is achieved, then the correction amplifier does notneed to provide the amplitude correction, and the workload of thecorrection amplifier is reduced.

The reference adjustment stage 403 is provided to achieve theseperformance objectives.

The potential amplitude imbalance at the terminals of the inductor is asa result of a potential amplitude imbalance between the output from theswitched supply 302 and the reference signal presented to the input ofthe correction amplifier 410 on line 316. Such amplitude imbalanceresults in a large current flowing in the inductor 402, particularly atlow frequencies. The amplitude adjustment block 404, forcing the inputto the feedback control stage 306 to be equal to the switched output online 302 at low frequencies, addresses this problem, as consequentiallythe voltage developed at the terminals of the inductors is then matched.

The amplitude adjustment block 404 adjusts the amplitude of thereference signal on line 316 in dependence on a correlation signal,which represents an amplitude error. The correlation signal is providedfrom the correlator 411 via the integrator 413. The thus amplitudeadjusted reference signal is provided by the amplitude adjustment clock404 as an input to the summer 408 and as an input to the differentiator406.

The control functionality provided by the reference adjustment stage 403is advantageous independent of whether the combiner stage 308 isimplemented as an inductor.

The two-fold functionality of the reference adjustment stage 403 can besummarised as follows.

One correlator output is used, by the amplitude adjustment block 404, tocontrol the amplitude of the signal provided to the differentiator andprovided as the output of the stage.

The other correlator output is used by the differentiator to providecontrol of the current through the inductor, to avoid the correctionamplifier having to provide current for the inductor.

An exemplary arrangement for the implementation of the second broadembodiment of the invention is now described with reference to FIG. 6.

With regard to FIG. 6, the arrangement of FIG. 5 is modified such thatthe feedback to the feedback control stage 306 is provided from theoutput of the correction amplifier rather than the output of theswitched supply stage. Thus, the feedback control stage 306 receives afeedback signal on line 602 which is derived from the output of thecorrection amplifier on line 412.

In this arrangement, the feedback control stage is modified, as thesubtractor 326 is not required. Thus the feedback signal on line 602forms the input to the PI control block 328, which forms an input to thesummer 330. The other input of the summer 330 is provided by the outputof the reference adjustment stage 402 as previously.

The arrangement of FIG. 6 illustrates a preferred exemplary arrangement,in which the reference adjustment stage 403 is provided, and thecombiner stage 308 is implemented as an inductor. However the principlesof providing a feedback signal for the feedback control stage 306 fromthe output of the correction amplifier is not limited to an arrangementin which the reference adjustment stage 403 is implemented, or in whichthe combiner stage 308 is implemented as an inductor. The referenceadjustment stage 403 may be omitted, and the combiner stage 308 may beimplemented by other means such as a transformer.

It should be noted that in various embodiments combinations of featuresare disclosed, and the invention is not limited in its applicability orimplementation to such combinations of features. Thus the broadprinciple described herein of the provision of a feedback signal from aninput to a combining stage is not limited to the specific implementationof the combiner stage. Similarly the implementation of the feedbacksignal from the input of the combiner stage to the switched supply stageis not limited to the implementation of a reference adjustment stage asillustrated herein.

Similarly advantages may be obtained by implementing the referenceadjustment stage described herein in a modulated supply stage,independent of the implementation of the combiner stage. Although thereference adjustment stage has particular advantages when combined withother features described herein, such as when the combiner stage isimplemented as an inductor, its usefulness is not limited to suchspecific implementations.

Still further it should be noted that the implementation of a combinerstage as an inductor is not limited to the specifics of any otheraspects shown herein. The implementation of the combiner stage as aninductor is not limited to an arrangement in which a feedback isprovided from an input of the combiner to the switched supply stage,although when used in combination with such feature advantages areobtained. Similarly the implementation of the combiner stages andinductor is not limited to any arrangement in which a referenceadjustment stage is provided, although again advantages may be obtainedby implementing the combiner stage as an inductor in combination withthe reference adjustment stage.

Finally it should be noted that the specific implementation of thefeedback from an input to the combiner to the switched supply stage isindependent of the specific implementation of the combiner stage and isindependent of whether or not a reference adjustment stage is provided.

With reference to FIG. 7, there is illustrated a multi-phase,multi-level supply arrangement in accordance with the principles ofexemplary embodiments described herein. The arrangement of FIG. 7utilises the feedback arrangement described in FIG. 3 hereinabove,wherein the feedback to the switched supply stage is provided from theoutput of the switched supply stage. In addition the arrangement of FIG.7 utilises the feature of the arrangement of FIG. 4 describedhereinabove, where the combiner stage 308 is implemented as an inductor.

In the illustrated multi-phase arrangement of FIG. 7, there is assumed adual-phase arrangement. Thus there is provided two sets of switchedsupply stages. Each switched supply stage corresponds to the switchedsupply stage 302 of earlier figures, and therefore in FIG. 7 there isillustrated a first switched supply stage 302 a, and a second switchedsupply stage 302 b, each of which correspond to the switched supplystages 302 of earlier figures. The switched supply controller 304provides a common switched supply control signal for the two switchedsupply stages 302 a and 302 b. As in the arrangement of FIG. 3, theswitched supply controller 304 receives an input signal from thefeedback control stage 306. The feedback control stage 306 receives thereference signal as an input on line 316, and additionally receives afeedback signal from the output of a switched supply stage. In theexample of a multi-phase arrangement, the feedback control stage 306requires only a single feedback signal from one of the switched supplystages. Thus in the arrangement of FIG. 7 there is illustrated theprovision of a feedback signal to the feedback control stage 306 fromthe output of the switched supply stage 302 a.

Each of the switched supply stages 302 a and 302 b provides an output toa respective combiner stage 308 a and 308 b. Each of the combiner stages308 a and 308 b may be implemented in accordance with any combiner stagepreviously described herein, in exemplary arrangements. In the preferredarrangement of FIG. 7 the combiner stages 308 a and 308 b areimplemented as inductors, identified as elements 402 a and 402 brespectively. The first terminal of each of the inductors 402 a and 402b receives the output signal from the respective switched supply stage302 a and 302 b. The second terminals of the inductors 402 a and 402 bare connected together to the output line 318.

The correction amplifier 410 receives the reference signal on line 316,and generates a current on line 412 which is injected at the output ofthe inductors 402 a and 402 b. Thus the output of the correctionamplifier 410 and the outputs of the inductors 402 a and 402 b areconnected in common to the output line, for delivery of output signal tothe load.

It will be understood from the foregoing description that each of thecombiner stages 308 a and 308 b may be implemented as transformers. Theoutputs of the respective transformers may be connected together inorder to provide the combined multi-phase signal on line 318.

It will be understood from the foregoing description that thearrangement of FIG. 7 may be modified so as to provide the feedbacksignal to the feedback control stage from the output of the correctionamplifier 410.

It will be apparent from the foregoing description that the arrangementof FIG. 7 may be further modified to include a reference adjustmentstage such as reference adjustment stage 403 illustrated in FIGS. 5 and6.

Each switched supply 302 a and 302 b may have an array of voltages, e.g.V₁ to Vx, where x can be any number from 2 upwards that is practicable.The switched supplies 302 a and 302 b are driven from the switchedsupply controller 304 which selects the nearest voltage.

In embodiments the switched supply controller 304 could be a PWM,Hysteretic or Delta sigma converter.

In a preferred arrangement the switched supplies 302 a and 302 b areclocked on opposite phases of a switching clock.

In accordance with the foregoing description there has been presented anumber of embodiments for implementing the invention. Various elementsof each embodiment may be utilised in isolation or in combination withother described elements. The invention is not limited to in its scopeto the specifics of any embodiment described herein. The scope of theinvention is defined by the appended claims.

What is claimed is: 1.-48. (canceled)
 49. A voltage supply stagecomprising: a selection means for selecting one of a plurality of powersupply voltages in dependence on a reference signal representing adesired power supply voltage; an inductor for combining the selectedpower supply voltage with a correction signal to generate an adjustedpower supply voltage, wherein a current representing the correctionsignal is injected at a second terminal of the inductor, a thus adjustedcurrent flowing in a load connected to the second terminal of theinductor to thereby develop the adjusted supply voltage across saidload; and a voltage-to-current converter adapted to generate thecorrection signal in dependence on the reference signal, wherein theselection means is arranged to select the one of the plurality of supplyvoltages further in dependence on a signal derived from the output ofthe voltage-to-current converter.
 50. The voltage supply stage accordingto claim 49 further comprising a feedback control stage for providingthe signal derived from the output of the voltage-to-current converter.51. The voltage supply stage according to claim 50 wherein the feedbackcontrol stage is adapted to receive as a first input the referencesignal and as a second input the output of the voltage-to-currentconverter, and further adapted to adjust the reference signal independence on the output of the voltage-to-current converter to providean adjusted reference signal for the selection means.
 52. The voltagesupply stage according to claim 51, wherein the feedback control stagecomprises: a proportional-integral, PI, controller for receiving theoutput of the adjusting means and generating a modified output, and asummer for adding the modified output of the PI controller to thereference signal, to form the output of the feedback control stage beingthe adjusted reference signal.
 53. The voltage supply stage according toclaim 49 further comprising a reference adjustment stage for adjustingthe reference signal to provide a modified reference signal.
 54. Thevoltage supply stage according to claim 53 wherein the selection meansis adapted to select in dependence on the modified reference signal. 55.The voltage supply stage according to claim 53 wherein the referenceadjustment stage adjusts the reference signal in dependence on a signalderived from the output of the voltage-to-current converter.
 56. Thevoltage supply stage according to claim 55 further comprising a feedbackcontrol stage adapted to receive as a first input the modified referencesignal and as a second input the output of the voltage-to-currentconverter, and further adapted to adjust the modified reference signalin dependence on the output of the voltage-to-current converter toprovide an adjusted modified reference signal for the selection means.57. The voltage supply stage according to claim 55 further comprising afeedback control stage adapted to receive as a first input the modifiedreference signal and as a second input the output of the selectionmeans, and further adapted to adjust the modified reference signal independence on the output of the selection means to provide an adjustedmodified reference signal for the selection means.
 58. The voltagesupply stage according to claim 53 wherein the reference adjustmentstage comprises circuitry for adjusting the amplitude of the referencesignal in dependence upon a difference between the amplitude of thereference signal and the amplitude of the output of thevoltage-to-current converter.
 59. The voltage supply stage according toclaim 58 wherein the circuitry for adjusting the amplitude of thereference signal includes: a correlator for determining the amplitudeerror between the reference signal and the amplitude of the output ofthe voltage-to-current converter; and an amplitude adjustment block formodifying the reference signal in dependence on said error.
 60. Thevoltage supply stage according to claim 53 wherein the referenceadjustment stage comprises circuitry for controlling a current flow inthe inductor to maximize current flow in the inductor and therebyminimize current flow in the voltage-to-current converter.
 61. Thevoltage supply stage according to claim 60 wherein the circuitry forcontrolling the current flow includes: a correlator for determining thecurrent flow in the inductor and for providing a control signal tomodify coefficients of a differentiator in dependence thereon, thedifferentiator being arranged to receive the reference signal andgenerate a differentiated version thereof.
 62. The voltage supply stageaccording to claim 61, wherein the differentiator is arranged to receiveas an input the amplitude adjusted reference signal generate adifferentiated amplitude adjusted reference signal, the referenceadjustment stage further comprising a summer for summing the amplitudeadjusted reference signal with the differentiated amplitude adjustedreference signal to form the modified reference signal.
 63. A trackingmodulated power supply stage for a mobile wireless device including thevoltage supply stage according to claim
 49. 64. A method for generatinga supply voltage comprising: selecting one of a plurality of powersupply voltages in dependence on a reference signal representing adesired power supply voltage; combining the selected power supplyvoltage with a correction signal in an inductor to generate an adjustedpower supply voltage, injecting a current representing the correctionsignal at the second terminal of the inductor; generating the correctionsignal as a current in dependence on the reference signal and theadjusted power supply voltage; and providing as a feedback signal thecorrection signal, and wherein an adjusted current flowing in a loadconnected to the second terminal of the inductor to thereby develop theadjusted supply voltage across said load wherein the selecting step isfurther arranged to select the one of the plurality of supply voltagesin dependence on the feedback signal.
 65. The method according to claim64 further comprising the step of controlling the feedback signal byreceiving as a first input the reference signal and as a second inputthe correction signal, and adjusting the reference signal in dependenceon the correction signal to provide an adjusted reference signal for theselecting step.
 66. The voltage supply stage according to claim 64further comprising a reference adjustment stage for adjusting thereference signal to provide a modified reference signal wherein thereference adjustment stage adjusts the reference signal in dependence ona signal derived from the output of the voltage-to-current converter,and further comprising a feedback control stage adapted to receive as afirst input the modified reference signal and as a second input theoutput of the voltage-to-current converter, and further adapted toadjust the modified reference signal in dependence on the output of thevoltage-to-current converter to provide an adjusted modified referencesignal for the selection means.
 67. The voltage supply stage accordingto claim 64 further comprising a reference adjustment stage foradjusting the reference signal to provide a modified reference signalwherein the reference adjustment stage adjusts the reference signal independence on a signal derived from the output of the voltage-to-currentconverter, and further comprising a feedback control stage adapted toreceive as a first input the modified reference signal and as a secondinput the output of the selection means, and further adapted to adjustthe modified reference signal in dependence on the output of theselection means to provide an adjusted modified reference signal for theselection means.
 68. The voltage supply stage according to claim 64wherein the reference adjustment stage comprises circuitry forcontrolling a current flow in the inductor to maximize current flow inthe inductor and thereby minimize current flow in the voltage-to-currentconverter.